Method for developing an electrostatic latent image

ABSTRACT

A METHOD FOR DEVELOPING AN ELECTROSTATIC LATENT IMAGE ON A PHOTOCONDUCTIVE SURFACE COMPRISING APPLYING A LIQUID DEVELOPER MATERIAL USING A POROUS MATERIAL TO SAID ELECTROSTATIC LATENT IMAGE ON SAID PHOTOCONDUCTIVE SURFACE, THE IMPROVEMENT COMPRISING APPLYING SAID LIQUID DEVELOPER MATERIAL TO SAID PHOTOCONDUCTIVE SURFACE USING SAID POROUS MATERIAL BY KEEPING AT LEAST A PORTION OF SAID POROUS MATERIAL IN CONTACT WITH A RESERVOIR OF SAID LIQUID DEVELOPER MATERIAL AND CONTACTING SAID PHOTOCONDUCTIVE SURFACE CONTAINIG SAID ELECTROSTATIC LATENT IMAGE THEREON WITH ANOTHER PORTION OF SAID POROUS MATERIAL AND THE IMPROVEMENT FURTHER COMPRISING SAID LIQUID DEVELOPER BEING A SUSPENSION OF A GRAFT PIGMENT IN AN INSULATING LIQUID IS DISCLOSED.

1974 MASAMICH I SATO ETAL 3,827,905

METHOD FOR DEVELOPING AN ELECTROSTATIC LATENT IMAGE Filed March 17, 1972 FIG.3

United States Patent 3 827 906 METHOD FOR DEVELbPING' AN ELECTROSTATIC LATENT IMAGE Masamichi 'Sato' and Yasuo Tamai, Asaki, Japan, assignors --to Fuji Photo Film (30., Ltd., Kanagawa, Japan Filed Mar. 17,1972, Set. No. 235,480

rClaims priority, application Japan, Mar. 17, 1971,

i .Int: Cl. G03g 13/10 US; Cl. 1 17 3 7.,.LE' 5 Claims 1 ABSTRACT OF DISCLOSURE A'metho'd fo'f developing an electrostatic latent image on a photoconduotive surface; comprising applying a liquid developer material using a porous material to said electrostatic latent image on said photoconductive surface, the improvement comprising applying said liquid developer material to said photoconductive surface using said porous materialby keeping at least a portion of said porous material in contact witha reservoir of. said liquid developer material and contacting saidphotoconductive surface containing said electrostatic latent image thereon with another portion of said porous material and the improvement further comprising said liquid developer being a suspension of a graft pigmentin an. insulating liquid is disclosed.

BACKGROUND OF THE INVENTION (1.) Field of, the *Invention This invention-relates to a xerographic development process wherein an improved easily handled liquid developer-is employed. Y

" (2) Description of the Prior Art One of the disadvantages with prior art xerographic developing systems using a liquid developer is that the liquid developer material utilized inwell known developingmachines'is.extremely volatile and combustible and, therefore, :cannotbe handled vin the machines without encountering the dangerof contamination or fire due to a portion of thedeveloper material splashing out of the machine;

ynnnar D scmP'rIoNoFiTHE. DRAWINGS FIG-.11 :is a schematic view of equipment for facsimile incorporating a xerographic developing apparatus.

FIGS Z (A) and 2(8) area longitudinal cross sectional view and a front view, respectively, of a simplified form of the meansemployed in practice ofthe method according to the invention." 4 jr'espondingi longitudinal cross sec:

FIG S. 3 16 6' are .c ol tional views showing various forms'of the means employed in practice ofthe method according to the present invention. I

In the figures, reference numeral 510 designates a pin tube, 11 a pin matrix, 12 a recording paper supply'roll,

13 an electrostatic recording a eema developing means, 20 a porous member, 21'-a container, '22 a liquid developer material carrying a suspension of graft pigment, 23

and 24 feed rollers, 25 and 26 squeeze rollers; 30 a porousmember, 31 a container, 32 an insulating liquid,- 40 to 43 transfer and back up rollers, 50 aistufling material, and 1 60a transfer roller. a

" SUMMARY OF THE'INVENTION Accordingly, the present invention provides a xerographic developing process using an easily handled liquid developer material of a suspensioriof a graft polymer in 3,827,906 Patented Aug. 6, 1974 suited for use in domestic or household facsimile printing systems which will come into widespread usage in the future.

DETAILED DESCRIPTION OF THE INVENTION Referring to the drawings, and particularly to FIG. 1, there is shown a facsimile printing apparatus embodying the present invention which comprises a pin tube 10 having a pin matrix 11, and a supply roller 12 for supplying a continuous web of electrostatic recording paper 13. As the electrostatic recording paper is drawn past the pin tube 10 having pin electrodes 11, electrostatic latent images are produced on the surface of the recording paper 13. During the passage through a developing apparatus 14 encircled by a dotted box, the electrostatic latent images thus produced by the pin electrodes are developed on the recording paper.

Such a recording paper and an electrostatic recording system using a pin tube are as well known in the art that, accordingly, a detail description thereof is omitted in this specification.

The present invention is particularly concerned with a development system suited for use in an apparatus, such as the one above described.

FIGS. 2 to 6 illustrate various forms of the means employed in practice of the method according to the present invention.

Referring now to FIGS. 2(A) and 2(8), which are a longitudinal cross section and a front view, respectively, showing a corresponding essential part of a simplified form of the means employed in the practice of the method according to the present invention, an elongated member 20 of a porous material is placed within a container 21, but with one end projecting from the top side of the container.

The lowermost part of the member 20 is dipped into a liquid suspension (liquid developer) 22 within the container. A portion of the liquid suspension in the container passes through the porous member due to capillary action and oozes out of the top end of the member projecting from the container.

A recording paper 13 containing electrostatic latent images thereon is moved by a pair of feed rollers 23 and 24 in contact with the top end face of the porous member 20- and then is passed between another pair of rollers 25 and 26 whereby any excess liquid on the surface of the recording paper is squeezed out.

It will thus be appreciated from the foregoing descripmember impregnated and saturated with a toner suspension.

However, such systems are well known in the art and are described, for example, in US. Pat. No. 3,343,956.

The method of the invention is entirely different from any of tho'se conventional systems in'that a liquid developer material carrying a graft pigment suspension is employedz- All'of the prior art developer materials were essentially suspensions of a mixture containing pigment and polymer suspended in'an insulating liquid. Such liquid suspensions, "however, cannot provide stability over-a long period of time in a uniformly dispersed condition.

More specifically, the toner particles in such a suspension-tend to adhere to the surfaces of the porous material and'the number of toner particles remaining suspended in the liquid developer'is significantly reduced over a long period of storage o'r'of use and finally becomes useless andmust be discarded. Accordingly, thed'eveloping system disclosed in the specification of the above cited US. patent is not suitable for use in domestic or household equipment because the apparatus involves the necessity of continually supplying the developer material to the developing system.

The present invention overcomes the above described problem by using a liquid developer material of a graft pigment suspension, that is one obtained by graft polymerization of an addition polymerizing monomer on the surfaces of the pigment particles.

It has been found by the inventors that the graft pigment which is suspended in an insulating liquid and is impregnated in the porous material, retains the ability to remain uniformly dispersed in the liquid suspension for a significantly longer period of time. The developer material consisting of a graft pigment suspension according to the present invention provides the ability for longer use or storage, such as, for example, over six months, as compared to the conventional liquid developer materials which, when impregnated in the porous material, normally becomes useless or inoperable in a few days.

The method of producing graft pigments is disclosed in Journal of the Society of Rubber Industry Japan, vol. 28, pp. 57-60 (1965).

Suitable such pigment-resin copolymers, are, for example, those described in US. Pat. No. 3,503,881. For example, a graft-copolymer obtained by the graftcopolymerization of carbon black and a monomer such as an acrylate represented by the following formula:

1 CHI-=4;

COO R:

wherein R represents H, CH or C H and R represents an alkyl group having from 6 to 19 carbon atoms, is described therein. This monomer component is capable of combining with carbon black and thereby dispersing carbon black grains in a carrier liquid.

Thus far the situation has been that, in a practical developer, sufficient charging characteristics cannot be provided by the graft-polymer alone in which the monomer (oleophilic) as described above is used.

Usually, a small amount of polar monomer is used in combination therewith was to improve the charging characteristics, and thus, copolymerization of carbon black and an oleophilic monomer and a polar monomer is conducted.

As such polar monomers, there are illustrated, e.g., acrylic acid, N,N diethylaminomethyl methacrylate, acrylonitrile, acrylamide, hydroxyethyl methacrylate, alpha-cyanomethyl acrylic acid, methacrylonitrile, N,N- diphenyl methacrylamide, zinc methacrylate, potassium maleate, etc.

When carbon black, the above-described monomers and a small amount of a polymerization initiator are added to a solvent and heated while stirring, polymerization occurs, and thus, the carbon black is graft-copolymerized with said monomers to obtain the so-called grafted carbon wherein carbon black and the resin components are combined with each other.

A .preferred graft pigment for the purposes of the present invention is Graft Carbon trade name of the Mitsubishi Gas Chemical Company, Incorporated, although other graft pigments produced from organic pigments may be used as developer materials in color reproduction. Those graft pigments are normally produced through a well-known process as disclosed in High Polymers Japan, The Society of Polymer Science, Japan, vol. 14, pp. 746-749 (1965)..

The use of graft carbon in conventional xerographic developer materials is now well known in the art and disclosed, for example, in Japanese Pat. 19,196/1969. I

In accordance with thepresent invention, the liquid developer material carrying a suspension of a graft pigment in a solvent is supplied through a porous material to the photoconductive surface containing electrostatic latent images therein.

4 It is believed that the stability over a long period of time of the graft pigment suspension impregnated in the porous material depends upon the dispersibility as well as the antiadhesion and absorption characteristics of the graft pigment to the porous material.

This will be more readily understood by considering I that when a liquid developer material of a conventional pigment suspension is impregnated in the porous material, the solvent in the developer material tends to vaporize as well as diffuse into the atmosphere. Atthe same time, some of the pigment particles in the developer material adhere to the surface of the porous member, with the result that the permeability of the pigment through the porous material is significantly reduced after a certain time period, due to such pigment particles intefering with the transfer of the remainder of the pigment through the porous material. I

Furthermore, the pigment permeability of theporous material cannot be recovered even were a fresh and new pigment suspension supplied and added to'the porous material. r

However, it has been found that the graft pigment suspension in accordance with this invention maintains a' sufficiently high degree of permeability in the porous material for a significantly longer time period. It has been found that when the porous material has been dried, the pigment transfer' can be recovered by supplying a fresh developer liquid to the porous member.

The porous member used in the process of this invention can be made of any desired porous material, such as felt, fiannelet, cloth, sponge, or bundle or fabric cloth of glass fibers.

Referring now to FIG. 3, another form of the means employed in practice of the method according to the invention is shown, which overcomes the problem described in the apparatus of FIG. 1, that is, contamination as a result of some of the toner material adhering to the photoconductive surface in the peripheral areas around the electrostatic image being developed on the surface as the liquid developer comes into direct contact with the dry photoconductive surface.

In the apparatus shown in FIG. 3, an additional porous material 30 is provided to apply a film of an electrically.

insulating liquid over the photoconductive surface containing the electrostatic latent image thereon prior to the supply of the liquid developer to the photoconductive surface, thereby preventing the toner material from adhering to the photoconductive surface as a result of forces other than the electrostatic charges contained in the photoconductive layer.

As a result, any contamination problems are substantially eliminated.

The porous member'30 may be formed of the same material as the porous member 20 of FIG. 2. The porous member 30 is dipped into the electric insulatingliquid 32 contained in a container 31." The insulating liqui'd'32 may be similar to the solvent of the above'described developer material, for example, materials such as cyclo;

hexene, Decalin, benzene, kerosene, isooctane, ligroin, methylcyclohexene, xylene, toluene, and combinations thereof, as well as other insulating materials can be used...

Referringto FIG. 4, there is shown a further modified form of the means employed in the practice of the method from several millimeters to ten millimeters in thickness (when measured in the direction of the advancement of the recording paper), tends to scrape or upset the powder image which is loosely held on the photoconductive surface during contact with'the'photoconductive surface of the recording paper moving across the end face'ofthe porous member in development, thus' resulting in an'inferior reproduction.

Another problem with the second means shown in FIG. 3 is contamination due to the production of a triboelectric charge on the photoconductive surface by frictional contact with the porous member 30- prior to the development of the electrostatic latent image, which holds some of the toner material on the surface of the recording paper.

Such problems of contamination are also found in conjunction with the developing apparatus of FIG. 2 (due to friction between the porous member 20 and the photoconductive surface containing the electrostatic charge therein). In the apparatus of FIG. 4, however, these problems are overcome and eliminated by forming a liquid film on the surface of an additional member by contacting the additional member with the porous member dipping in the liquid developer and then transferring the liquid film from the surface of the additional member to the photoconductive surface Without any relative motion between the member and the photoconductive layer and without direct contact with the porous member.

The means shown in FIG. 4 further includes transfer rollers 40 and 41 rotating in contact with the top end faces of the porous members 20 and 30, respectively. These rollers are constructed of a material which is capable of carrying and retaining an amount of liquid material thereon. Preferably, the rollers are metal or plastic rollers having a rough or coarse outer surface, alternatively, having a planar outer surface covered with a rough surfaced material such as mesh, cloth, sponge, felt, flannel, or paper.

As will be understood by those skilled in the art, metal rollers also can serve as a development electrode.

Take up or feed rollers 42 and 43 formed of metal or rubber are provided in the third means.

Accordingly, any triboelectric contamination problems can be substantially eliminated by rotating the rollers 40 and 41 without relative motion or slippage between the surfaces of the rollers and the photoconductive surface containing the electric static latent image therein.

Referring to FIG. 5, a cross sectiional view of a still further means embodying the present invention is shown, which eliminates the common problem of all of the above described apparatus, that is, the tendency of the liquid developer material to seep out of the porous member and away from the container when the container is overturned.

In the apparatus of FIG. 5, the container is packed with a stufiing material 50' such as cotton, cloth, paper or fibers, which prevents the developer material from seep ing out of the container.

In FIG. 6, there is shown still another means employed in the practice of the method according to the present invention, which further includes a roller 60 adapted to transfer a film of the developer material from the porous member to the photoconductive surface of the recording paper, preventing a direct contact of the porous member with the photoconductive surface. The roller may be formed of a material similar to that of the roller 40 described.

The existence of the roller 60 assures a more uniform thickness of the developer liquid film formed on the photoconductive surface. Preferably, the roller '60 is adapted to rotate in the same direction as the rotation of the roller 40. Rotation of the rollers in the same direction will facilitate a uniform distribution of the toner on the roller 60.

What is claimed is:

1. In a method for developing an electrostatic latent image on a photoconductive surface comprising applying a liquid developer material using a porous material to said electrostatic latent image on said photoconductive surface, said liquid developer material being applied to said photoconductive surface using said porous material by keeping at least a portion of said porous material in contact with a reservoir of said liquid developer material and contacting said photoconductive surface containing said electrostatic latent image thereon with another portion of said porous material, the improvement comprising said liquid developer being a suspension of a graft pigment in an insulating liquid.

2. The method of claim 1, wherein said contacting is by indirectly contacting said photoconductive surface with said porous material using an additional surface adapted to transfer said developer material from said porous material to said photoconductive surface.

3. The method of claim 1, wherein said porous material is felt, flannelet, cloth, sponge, glass fiber bundle or glass fiber cloth.

4. The method of claim 1, wherein said insulating liquid is cyclohexene, Decalin, benzene, kerosene, isooctane, ligroin, methylcylohexene, xylene, toluene or mixtures thereof.

5. The method of claim 1, wherein said graft pigment is graft carbon.

References Cited UNITED STATES PATENTS 3,551,146 12/1970 Gundlach 11737 LE 3,503,881 3/1970 Shinohara et al 25262.1 3,629,117 12/1971 Okuno 25262.1 3,639,243 2/ 1972 Okuno 25262.1 3,639,244 2/1972 Machida et al. 25262.1 3,102,045 8/1963 Metcalfi et a1 117-37 LE 3,133,484 5/1964 Wright 117-37 LE 3,343,956 9/1967 Wright 961 R MICHAEL SOFOCLEOUS, Primary Examiner US. Cl. X.R. 

